1. Field of the Invention
This invention relates generally to rupturable pressure relief apparatus, and more particularly, but not by way of limitation, to rupturable pressure relief apparatus which rupture at very low pressure differentials in both the normal and reverse rupture modes.
2. Description of the Prior Art
A variety of rupturable pressure relief apparatus have been developed and used heretofore. Generally, these devices include a rupture disk supported between a pair of complementary support members or flanges which are in turn connected to a relief connection in a vessel or system containing fluid pressure. When the fluid pressure within the vessel or system exceeds the design pressure of the rupture disk, rupture occurs allowing fluid pressure to be relieved from the vessel or system.
Most of the rupturable pressure relief apparatus of the prior art is designed for failure in one direction. That is, the apparatus is installed in a pressurized system between first and second pressure zones, so that when excess pressure occurs in the first zone, it is vented to the second zone. This is referred to as the "normal rupture mode".
In some applications of rupturable pressure relief apparatus it is not only necessary that the apparatus relieve fluid pressure in the normal rupture mode, i.e., from the first zone to the second zone, but also that the apparatus relieve fluid pressure in the reverse direction, i.e., from the second zone to the first zone. This is referred to as the "reverse rupture mode". An example of an application where the rupturable pressure relief apparatus must relieve fluid pressure in both directions is where the apparatus is installed on a vessel containing heated fluid under pressure. If the fluid pressure within the vessel becomes too high, the pressure relief apparatus must rupture in the normal rupture mode. On the other hand, if a vacuum is created within the vessel, such as by the rapid cooling of the fluid therein or the rapid withdrawal of fluid therefrom, the apparatus must relieve fluid pressure in the reverse rupture mode to protect the vessel from excess internal vacuum and the consequent damage thereto such as the collapse of the vessel. Many other applications requiring rupturable pressure relief apparatus having the ability to relieve excess pressure in both directions exist.
While rupturable pressure relief apparatus have been developed and utilized heretofore which relieve excess pressure in both the normal and reverse rupture modes, such devices are generally limited to applications where relatively high pressure differentials are exerted on the apparatus before rupture occurs. For example, U.S. Pat. No. 3,091,359 to Wood discloses such a device. The minimum rupture pressures which can predictably be achieved by the device of U.S. Pat. No. 3, 091,359 are relatively high, and experience has shown that the '359 apparatus will provide a total rupture of both of its rupture disks in the reverse rupture mode only if the design rupture pressure in the normal rupture mode is not greater than twice the design rupture pressure in the reverse rupture mode.
U.S. Pat. No. 4,301,938 to Wood et al. is directed to a similar safety pressure relief device which can relieve fluid pressure in either direction at relatively low pressure differentials. However, the device of the '938 patent is still not suitable for use in applications where very low pressure differentials are involved, and as is the case in all such prior art apparatus wherein metal and plastic parts are utilized, problems occur which are brought about by the premature cutting of the plastic parts by sharp edges on the metal parts. Metal parts which include apertures, slits, slots and other configured openings formed therein very often also include sharp raised portions or burrs brought about by the manufacturing operation. When such metal parts are positioned adjacent plastic parts in a rupturable pressure relief apparatus, the fluid pressure exerted on the parts during operation of the apparatus cause the sharp edges or burrs to puncture or weaken the plastic parts and the consequent premature failure of the apparatus.
By the present invention improved rupturable pressure relief apparatus are provided which obviate problems associated with the cutting or weakening of plastic parts by the sharp edges of metal parts and which are particularly suitable for applications where rupture and pressure relief must occur at very low pressure differentials in both the normal and reverse rupture modes.